Circuit arrangement for protection against electrostatic discharges and a method for operating same

ABSTRACT

A circuit arrangement for protection against electrostatic discharges has a diverting structure, which includes a diverting element and a switchable element. The diverting element can be set up to drain off an electrostatic discharge between a first and a second terminal. The switchable element can take a first and a second switching state, where a function of the diverting element can be activated depending on the switching state of the switchable element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/675,833, filed Sep. 22, 2010, which is a 35 U.S.C. §371 NationalStage Entry of International Patent Application No. PCT/EP2008/061035,filed Aug. 22, 2008, which claims the priority of Germany PatentApplication No. 102007040875.9, filed Aug. 29, 2007, each of which isincorporated herein by reference in its entirety for all purposes.

FIELD OF THE INVENTION

The invention concerns a circuit arrangement for protection againstelectrostatic discharges and a method for operating such a circuitarrangement.

BACKGROUND OF THE INVENTION

When there are electrostatic discharges (ESD), high voltages occur, forexample between the terminals of an electric circuit. This can lead tohigh currents through the circuit. Particularly with integratedcircuits, the circuit could be destroyed by this.

To protect a circuit against electrostatic discharges it is possible toprovide circuit arrangements that can drain off a current if there is anelectrostatic discharge, thus protecting the electric circuit fromdamage if a high voltage occurs.

In such circuit arrangements it is possible to use various types ofdiverting elements, which are in each case connected between theterminals of the circuit or a component that is to be protected. Thevarious types differ, among other things, in their voltage-currentcharacteristic curves, and accordingly can have different protectivebehaviors.

FIG. 14 shows an example of a voltage-current diagram with thevoltage-current characteristic curves of different diverting elements,which here are represented as so-called transmission line pulsing (TLP)curves. For example, a first type of diverting element has thecharacteristic curve SFA, which has the form of a diode characteristicwith breakdown voltage VB. The characteristic curve SPA does not have avoltage snapback. In contrast, a second example of a diverting elementis determined by the characteristic curve SA, which has snapback fromthe breakdown voltage VB to a snapback voltage VR.

Protection of the circuit or component may additionally be necessary invarious operating states. For example, a component in uninstalled stateshould be protected, for example against a discharge due to anelectrostatic charge transferred to the component by contact and/orstatic electricity due to friction. Such protection in which a componentin uninstalled state is protected can also be called chip-levelprotection. Moreover, it may be necessary to protect a component fromovervoltages that occur at terminals of the component when it isinstalled in a circuit and/or when it is operated together with acircuit. Such overvoltages can occurs, for example, due to undesiredtransient processes, for instance at power supply lines or because ofelectrostatic discharges. Protection of a component in installed stateor during the operation of the component can also be called system-levelprotection.

Accordingly, protective elements or protective structures for protectionagainst electrostatic discharges can basically be better suited for oneof several possible protective applications. Referring to the diagram inFIG. 14, for example, with a protective element having a characteristiccurve corresponding to curve SA, the protective element, when operatedat a supply voltage or a battery voltage VBAT, may become damaged ifthere is an overvoltage that is to be drained off. If, for example, avoltage between the terminals to be protected is higher than thebreakdown voltage VB, the protective element is triggered, whichinitially causes a snapback to the snapback voltage VR. If, as in thisexample, the battery voltage is higher than the snapback voltage VR, theprotective element is, however, no longer in a nonconducting state, butrather there will be a current increase up to a value that correspondsto the battery voltage VBAT. As a rule, this current will be higher thanthe permissible continuous current of the protective element, which inthe end can lead to damage to the protective element.

Such a damaged protective element may effect a permanently conductingconnection between the terminals to be protected. As a consequence, thedevice to be protected or the circuit to be protected possibly can nolonger be used.

If protective elements with a snapback-free curve corresponding to curveSFA in FIG. 14 are used, as a rule, a considerably larger area isrequired on a semiconductor chip than in the case of a protectiveelement with a curve corresponding to curve SA. This leads to highercost and/or a larger circuit in the production of a component with acorresponding protective element. As a rule, this also involves highercosts.

SUMMARY OF THE INVENTION

It is a problem of the invention to specify a circuit arrangement forprotection against electrostatic discharges with which a circuit that isto be protected can be operated in various operating states reliably andwith low cost. It is also a problem of the invention to specify a methodfor operating such a circuit arrangement that can be realized at lowcost.

In an embodiment example, a circuit arrangement for protection againstelectrostatic discharges has a first diverting structure. The firstdiverting structure comprises a first diverting element, which isdesigned to drain off an electrostatic discharge between a first and asecond terminal, and a first switchable element, which can take a firstand a second switching state. The function of draining off of theelectrostatic discharge of the first diverting element is activated bythe first switching state of the first switchable element anddeactivated by the second switching state of the first switchableelement. In other words, a function of the first diverting element canbe activated depending on the switching state of the first switchableelement. In addition, a second diverting structure with a seconddiverting element, which again connects the first and second terminalstogether, is to be provided. The second diverting element is made, forexample, as an element with a voltage-current characteristic curve thatdoes not have voltage snapback.

Therefore, a function, in particularly a protection function of thefirst diverting element, can be activated for the case when the firstdiverting element is suitable for a relevant operating state of thecircuit that is to be protected. Accordingly, the function of the firstdiverting element can also be intentionally deactivated. For example,this can prevent a triggering of the first diverting element leading todamage of the diverting element and to an adverse effect on thefunctioning of the circuit to be protected. Therefore, both theprotection and the functioning of a circuit to be protected can beguaranteed for different operating states, for example chip-levelprotection and/or system-level protection. Activation or deactivation ofthe first diverting element takes place in accordance with an alteredswitching state of the switchable element. Consequently, the cost forproviding the circuit arrangement and for the operation of the circuitarrangement is low.

For example, the second diverting element is likewise set up to drainoff an electrostatic charge between the first and the second terminal,in particular for an operating state in which a function of the firstdiverting element is deactivated. In this case, for example, the firstdiverting element is suitable for chip-level protection and the seconddiverting element is suitable for system-level protection.

For example, the diverting element can be designed as an element with avoltage-current characteristic that has voltage snapback. To preventdamage to the diverting element for the case when the circuitarrangement is operated with a voltage that is higher than the snapbackvoltage of the diverting element, the diverting element can, forexample, be connected in a series circuit with the switchable element ofthe first and second terminal, whereby the switchable element is in anonconducting state when an operating voltage is applied. Thus, thefunction of the diverting element is also not active.

The switchable element in this case can be designed as a switch ormultiply switchable element, or alternatively as a one-time switchableor irreversibly switchable element. In one embodiment example theswitchable element is a fuse, which becomes damaged in the case of toohigh a current through the diverting element and the fuse, and with thatprevents the further flow of current through the diverting element thatcould lead to damage to the diverting element.

Optionally, a second diverting structure with a second diverting elementthat again connects the first and second terminals together can also beprovided. For example, the second diverting element is set up to drainoff an electrostatic discharge between the first and second terminal, inparticular for an operating state in which a function of the firstdiverting element is deactivated. The second diverting element isdesigned for this, for example, as an element with a voltage-currentcharacteristic that does not have voltage snapback. In this case, forexample, the first diverting element is suitable for chip-levelprotection and the second diverting element for system-level protection.

In another embodiment, a first and a second diverting element are eachconnected in a series circuit with a switchable element between thefirst and the second terminal. The first and second diverting elementsin this case are preferably set up to drain off electrostaticdischarges, each in different operating states, for example the firstdiverting element is provided for chip-level protection and the seconddiverting element for system-level protection. In addition, a controlcircuit is provided, which, by controlling the switchable elements,activates in each case one of the diverting elements from among of thefirst and second diverting elements and that in each case deactivatesthe other diverting element from the said elements. The activation ordeactivation in this case takes place, for example, in accordance withan operating state established by the control circuit.

The one-time switchable element or fuse can be destroyed, for example,if a protection operation occurs due to an appropriate current flow.Alternatively, depending on the control signal a current flow throughthe one time-switchable element can be produced that leads todestruction of the switchable element, thus to separation of theconducting connection through the switchable element.

In another embodiment example, a circuit arrangement for protectionagainst electrostatic discharges has a diverting structure. Thisdiverting structure comprises a diverting element that is set up todrain off an electrostatic discharge between a first and a secondterminal. In addition, in the circuit arrangement there are provided afirst and a second trigger element, which issue trigger signals that aresuitable for controlling a diverting element. In particular, the firsttrigger element is set up to issue a first trigger signal in accordancewith a preset voltage increase between the first and second terminal.The second trigger element is set up to issue a second trigger signal inaccordance with a preset threshold voltage between the first and secondterminal. The diverting element is set up to connect the first andsecond terminals in accordance with the first and/or the second triggersignal. Accordingly, the first and second trigger elements arepreferably designed for different operating states, for example againfor chip-level protection and system-level protection. Via a controlcircuit and appropriately arranged switchable elements, a function ofthe first and second trigger elements can in each case be activated ordeactivated. Thus, depending on an established operating state anappropriate triggering of the protection can take place, so that anundesired or unnecessary triggering of the diverting element can beprevented.

In one embodiment example of a method for operating a circuitarrangement for protecting against electrostatic discharges, the circuitarrangement is provided with a first and a second diverting element,which are set up to drain off an electrostatic discharge between a firstand a second terminal. In this case a draining off function of thesecond diverting element is permanently activated or becomes activatedor deactivated in accordance with an activation state of the protectionfunction of the first diverting element. The operating state of thecircuit arrangement is determined, and a protection function of thefirst diverting element is activated and/or deactivated in accordancewith the determined operating state.

For example, the activation and/or the deactivation takes place via aswitchable element that connects the first terminal to the secondterminal in a series circuit with the first diverting element.Deactivation of a protection function of the first diverting element inthis case can take place irreversibly.

In another embodiment example of the method, again a circuit arrangementis provided with a first and a second diverting element, which are setup to drain off an electrostatic discharge between a first and a secondterminal. A first trigger signal is generated in accordance with apreset voltage rise between a first and a second terminal. In addition,a second trigger signal is generated in accordance with a presetthreshold voltage between the first and the second terminal. Theoperating state of the circuit arrangement is determined. The firsttrigger signal is transmitted if a first operating state is determinedin the determination of the operating state and the second triggersignal is transmitted if a second operating state is determined in thedetermination of the operating state. The diverting element iscontrolled with the transmitted trigger signal.

In the relevant embodiment examples of the method, an average potentialdifference between the first and second terminal can be evaluated in thedetermination of the operating state.

The various embodiment forms are based on the common idea ofguaranteeing a matched protection against electrostatic discharges invarious operating situations, in particular in a system-level operatingstate and in a chip-level operating state. In other words, electrostaticdischarges that originate from different causes can be drained off withthe described embodiment forms.

BRIEF DESCRIPTION OF THE DRAWINGS

In what follows, the invention will be explained in detail by means ofembodiment examples with reference to the drawings. Elements with likefunction or activity have the same reference numbers.

FIG. 1 shows a first embodiment example of a circuit arrangement forprotection against electrostatic discharges,

FIG. 2 shows a second embodiment example of a circuit arrangement forprotection against electrostatic discharges,

FIG. 3 shows a third embodiment example of a circuit arrangement forprotection against electrostatic discharges,

FIG. 4 shows an exemplary voltage-current diagram,

FIG. 5 shows an embodiment example of a fuse,

FIG. 6A shows a fourth embodiment example of a circuit arrangement forprotection against electrostatic discharges,

FIG. 6B shows a fifth embodiment example of a circuit arrangement forprotection against electrostatic discharges,

FIG. 7 shows a sixth embodiment example of a circuit arrangement forprotection against electrostatic discharges,

FIG. 8 shows a seventh embodiment example of a circuit arrangement forprotection against electrostatic discharges,

FIG. 9 shows an eighth embodiment example of a circuit arrangement forprotection against electrostatic discharges,

FIG. 10 shows a ninth embodiment example of a circuit arrangement forprotection against electrostatic discharges,

FIG. 11 shows a tenth embodiment example of a circuit arrangement forprotection against electrostatic discharges,

FIG. 12 shows an eleventh embodiment example of a circuit arrangementfor protection against electrostatic discharges,

FIG. 13 shows an embodiment example of trigger elements, and

FIG. 14 shows an exemplary voltage-current diagram for differentdiverting elements.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment example of a circuit arrangement forprotection against electrostatic discharges with a diverting structureESD1, which is connected between a first and a second terminal K1 andK2. The diverting structure ESD1 comprises a first diverting elementDE1, which is represented symbolically in FIG. 1 by a transistor. Thediverting structure ESD1 additionally comprises a switchable elementSW1, which can take a first and a second switching state. The divertingelement DE1 is set up to drain off an electrostatic discharge betweenthe first and the second terminal K1 and K2. Here a function, inparticular a diverting function of the diverting element DE1, depends onthe switching state of the switchable element SW1. In addition to asemiconductor element that can drain off electrostatic discharges, thediverting element DE1 can also have one or more trigger devices thatcontrol a protection operation via a diverting element DE1.

In various embodiment examples, the switchable element SW1 can beintended to drain off an electrostatic discharge between the first andsecond terminal K1 and K2 directly in one possible current path, so thatif switchable element SW1 is in an open, nonconducting state, aprotection function is deactivated. In other embodiment examples, thefunction of one or more trigger elements is also controlled, inparticular, activated or deactivated by the switchable element SW1.

FIG. 2 shows another embodiment example of a circuit arrangement forprotection against electrostatic discharges in which the divertingelement connects the first terminal K1 to the second terminal K2 in aseries circuit with the switchable element SW1. The switchable elementSW1 in this embodiment example is designed as a one-time-switchable orirreversibly switchable element. For example, the one-time-switchableelement comprises a fuse.

The diverting element DE1 comprises, for example, an NPN transistor oran n-channel field effect transistor. Alternatively, the divertingelement could also comprise a thyristor or a silicon-controlledrectifier (SCR). In another embodiment example, the diverting elementDE1 can also comprise an element with a voltage-current characteristicthat has voltage snapback. This is symbolically represented in FIG. 2 bythe characteristic curve of the diverting element DE1. The divertingelement DE1 has, for example, a characteristic that corresponds to thecharacteristic SA in the diagram in FIG. 14.

If the circuit arrangement is operated with a circuit connected toterminals K1 and K2 that is connected to a supply voltage that isgreater than a snapback voltage VR of the diverting element DE1, ifdiverting element DE1 is triggered there could be current flow thatleads or would lead to damage to diverting element DE1. Such current,which results not only from the ESD load, but also from the voltagedifference between the supply voltage and the withstand voltage ofdiverting element DE1, also, however, causes burnout of the one-timeswitchable element SW1, due to which current flow is interrupted. Inthis case the diverting element DE1 itself can remain undamaged. Inparticular, damage to the diverting element DE1 does not occur since thefirst and second terminals K1 and K2 are not permanently electricallyconnected together. The circuit connected to terminals K1 and K2 thuscontinues to be functional. However, a permanent electrical connectionof the first and second terminals K1 and K2 is effectively avoided evenif the diverting element DE1 is destroyed since the switchable elementSW1 is not conducting.

Diverting elements having a current-voltage characteristic with voltagesnapback are especially suitable for protecting a circuit againstelectrostatic discharges that are produced by contact and staticelectricity. Such protection is especially meaningful for componentsthat are not yet incorporated into a circuit or are not yet operatedwith such a circuit, and can also be called chip-level protection.Through the burnout or opening of the one-time switchable element SW1,the circuit to be protected can be protected against electrostaticdischarges in the uninstalled state. However, since the loss ofprotection occurs when the component is installed, the loss ofprotection may be unimportant.

However, in order to be able to drain off even electrostatic dischargesduring the operation of a circuit, which corresponds to system-levelprotection, another embodiment example shown in FIG. 3 features is asecond diverting structure ESD2 with a second diverting element DE2,where the second diverting element DE2 connects the first terminal K1 tothe second terminal K2. The second diverting element DE2 comprises, forexample, a PNP transistor or a P-channel field effect transistor or aZener diode. In other words, the second diverting element DE2 cancomprise an element with a voltage-current characteristic that does nothave snapback. Such an element is particularly suitable for system-levelprotection against electrostatic discharges during the operation of aconnected circuit that is to be protected.

As described above for the embodiment example in FIG. 2, if the firstdiverting element DE1 is triggered, destruction of the first switchableelement designed as a safety device can occur if an operating voltage atterminals K1 and K2 is higher than the snapback voltage VR of the firstdiverting element DE1. However, protection against electrostaticdischarges is additionally guaranteed by the second diverting structureESD2. In other words, after destruction of protection SW1 there stillremains ESD protection of a circuit to be protected even if a protectionfunction of the first diverting element DE1 is deactivated.

FIG. 4 shows an exemplary voltage-current diagram during the occurrenceof an electrostatic discharge, at the beginning of which both the firstand the second diverting elements DE1 and DE2, in accordance with theembodiment example in FIG. 3, are activated. Here, there is firstvoltage snapback via the first diverting element DE1 and a subsequentrise of voltage in current through the first diverting element DE1. Inthe region indicated by FU there is destruction of the safety deviceSW1, where the first diverting element DE1 can also be destroyed.Accordingly, farther drainage of the electrostatic discharge can takeplace via the second diverting element DE2, whose characteristic isshown with a broken line. After this operation, which is irreversible asa rule, further drainage of electrostatic discharges takes place onlyvia the second diverting element DE2.

FIG. 5 shows an embodiment example of a fuse that can be used asswitchable element SW1 in one of the embodiment examples that are shown.Such a fuse can be realized, for example, in the layout of asemiconductor circuit. If there is a corresponding current load on thefuse, the narrow points in the shaded region of the fuse come apartbecause of the high current, so that then there is no electricalconnection between the two metal regions shown.

In the embodiment examples shown in FIGS. 2 and 3, the switchableelement or safety device SW1 can be destroyed or opened by theoccurrence of an electrostatic discharge. In the embodiment examplesshown in FIG. 6A, a bypass circuit BR designed as a transistor, which isconnected in parallel with the first diverting element DE1, is provided.Transistor BR has a control terminal BL via which a control signal canbe delivered.

Depending on the control signal, the controlled paths of transistors BRcan thus be connected in a conducting state, through which the first andsecond terminals K1 and K2 are connected via the first switchableelement SW1. If there is an appropriate voltage between terminals K1 andK2, there will correspondingly be current flow through safety deviceSW1, which destroys safety device SW1 and thus deactivates theprotection function of the first diverting element DE1. The firstdiverting element DE1 itself is not destroyed. The control signal atcontrol input BL can be generated by means of appropriate detectiondevices such as a power-on-reset (POR), an overvoltage detectioncircuit, an EPROM circuit, or directly from a digital core of anintegrated circuit to be protected.

FIG. 6B shows another embodiment example of a circuit arrangement forprotection against electrostatic discharges, in which, in contrast tothe embodiment example in FIG. 6A, the first diverting element DE1 andthe safety device SW1 are exchanged with each other. Moreover, similarto the embodiment example in FIG. 3, a second diverting element DE2 isprovided between the first and second terminal K1 and K2. Thus, again aprotection function against electrostatic discharges is guaranteed, evenif the first diverting element DE1 is disconnected as a result ofdestruction of safety device SW1 or its function is deactivated. Thesecond diverting element DE2 is permanently activated with regard to itsprotection function, both in this embodiment example and in theembodiment example in FIG. 3.

FIG. 7 shows another embodiment example of a circuit arrangement forprotection against electrostatic discharges, in which the firstdiverting element DE1 has a control input T1 for feed of a controlsignal, in accordance with which the conduction of the first divertingelement DE1 can be controlled. The control input T1 is connected to thecontrol terminal BL for feed of the control signal.

The diverting element DE1 is actively triggered during operation by thecontrol signal. At the corresponding voltages on terminals K1 and K2, acurrent flows through the series-connected safety device SW1 that is solarge that SW1 burns out. For example, thyristors, particularly theso-called silicon-controlled rectifiers (SCR), turn-on bigFET divertingelements or other active turn-on diverting elements with and withoutsnapback can be used as actively triggerable diverting elements.

In another embodiment example, a second diverting element DE2 can beconnected in parallel with the circuit shown in FIG. 7, for example asin the embodiment example in FIG. 3.

As explained above, for different operating states of a circuit that isto be protected, different diverting elements with different protectioncharacteristics can be used, each of which is matched to one of theintended operating states. FIG. 8 shows an embodiment example of acircuit arrangement for protection against electrostatic discharges, inwhich arrangement a first and a second diverting structure ESD1 and ESD2are connected between the first and second terminals K1 and K2. Thefirst diverting structure ESD1 in this case has a series circuit of afirst switchable element SW1 and a first diverting element DE1, whichpreferably comprises an element with a voltage-current characteristicthat has voltage snapback. The second diverting element ESD2 accordinglycomprises a series circuit of a second diverting element DE2 and asecond switchable element SW2, whereby the second diverting element DE2preferably comprises an element with a voltage-current characteristicthat does not have snapback. The first and second terminals K1 and K2are each connected via the series circuit of the switchable elements SW1and SW2 and the diverting elements DE1 and DE2. The circuit arrangementadditionally has a control circuit CTRL, which is connected to the firstand second terminals and has a control output, which is connected to thefirst and second switchable elements SW1 and SW2 for control.

The control circuit CTRL is set up to activate, via control of the firstand second switchable elements SW1 and SW2 with the correspondingactivation signals EN, EN, one diverting element each from among of thefirst and second diverting elements DE1 and DE2, and to deactivate therelevant other diverting element from said elements.

The control circuit comprises, for example, a detection circuit fordetermining an operating state of the circuit arrangement or the circuitto be protected. Such a detection circuit comprises, for example, apower-on-reset (POR switch), a poly-fuse, an EPROM or other comparablecircuit. For example, an average potential difference between the firstand second terminals K1 and K2 is evaluated through the control circuitCTRL.

The switchable elements SW1 and SW2 can be designed as one-timeswitchable elements, and in this case the first switchable element SW1is switchable one time from a conducting to a nonconducting state andthe second switchable element SW2 can be switched one time from anonconducting state to a conducting state. In other words, the firstdiverting element DE1 can be deactivated once and the second divertingelement DE2 can be activated once. This can, for example, be meaningfulfor the case when the first diverting element DE1 is intended forprotection of a component in the uninstalled state, chip-level state,and the second diverting element DE2 is intended for protection of thecomponent in the installed state, system-level state.

However, the first and second switchable elements SW1 and SW2 can alsobe designed as multiply switchable elements and can comprise, forexample, a transmission gate or a p-channel field effect transistor orbipolar transistors. Therefore, it is possible even to guaranteeprotection of a component that is installed and uninstalled or put intooperation and taken out of operation a number of times.

There are several possibilities for active triggering of ESD divertingelements. Various trigger elements can be used for this. The triggerproperties of some of these trigger elements are better suited forchip-level ESD protection in which the component to be protected is tobe protected, for example, from electrostatic discharges due to contact.On the other hand, the trigger properties of other trigger elements canbe better suited for system-level ESD protection, which is intended toprotect a component in the installed state and/or in the operation ofthe component.

For example, trigger elements can be set up to detect a rapid rise ofvoltage between terminals to be protected, in order to initiate, inaccordance with this, a triggering, whereby the triggering is dependenton a specific rise time of the monitored signal at the terminals to beprotected. Such triggering can be carried out, for example, with atrigger element that has an RC member for detection. A trigger elementwith an RC member accordingly can also be called an RC rise timetrigger. However, transient disturbances occurring during normaloperation or system-level operation at the protected terminals caninitiate an undesired triggering.

A trigger element that is suitable for system-level protection is setup, for example, to detect the exceeding of a preset threshold voltagebetween the monitored terminals and to initiate triggering if thethreshold voltage is exceeded. Usually such a trigger element does notrespond if there are brief voltage peaks, and for this reason it is lesssuitable for chip-level protection.

FIG. 9 shows another embodiment example of a circuit arrangement forprotection against electrostatic discharges, which has a divertingstructure ESD1 with two control inputs for feed of a first and secondcontrol signal TEN1 and TEN2. The control signals TEN1 and TEN2 areissued by a control circuit CTRL.

The diverting structure ESD1 has, for example, a diverting element, afirst trigger element, which is suitable for chip-level protection, anda second trigger element, which is suitable for system-level protection,not shown here for the sake of clarity. For example, the first triggerelement can be activated or deactivated by the first control signalTEN1. Accordingly, the second trigger element can also be activated ordeactivated by the second control signal TEN2. The control signal CTRLcan thus activate the appropriate trigger element depending on theprotection required, namely chip-level protection or system-levelprotection, and deactivate the other trigger element. In triggering theactivated trigger element, the corresponding trigger signal is used tocontrol the diverting element or is transmitted further on. In otherwords, the diverting element depends on the trigger signal forelectrically connecting the first and the second terminals K1 and K2 inorder to drain off the electrostatic discharge.

For example, the first trigger element is set up to issue a firsttrigger signal in accordance with a preset voltage rise between thefirst and second terminals K1 and K2, while the second trigger elementis set up to issue a second trigger signal in accordance with the presetthreshold voltage between the first and second terminals. The first andsecond trigger elements can each be activated or deactivated by a firstand a second switchable element, whereby the switchable elements arecontrolled by control signals TEN1 and TEN2.

For a circuit arrangement in accordance with this embodiment example, itcan be meaningful to use as the diverting element a PNP transistor, ap-channel field effect transistor, a Zener diode, or generally anelement with a voltage-characteristic that does not have snapback. Theoperating state of the circuit to be protected can be determined, forexample, by evaluating an average potential difference between the firstand second terminals K1 and K2. Thus, by means of the average potentialdifference it can be determined if chip-level protection or system-levelprotection is needed.

FIG. 10 shows another embodiment example of such a circuit arrangement,which is based on the embodiment example in FIG. 9. The circuitarrangement comprises a first trigger element TR1 and a second triggerelement TR2, each of which is electrically connected to the first andsecond terminals K1 and K2 for monitoring the potential conditions.Additionally provided are a first and a second switchable element SW1and SW2, which in this embodiment example are designed as AND elements.In each case a first input of the AND elements SW1 and SW2 is set up tofeed a corresponding control signal TENT or TEN2 from the controlcircuit CTRL, while a second input is connected to the correspondingtrigger outputs TA1 and TA2 of the first and second trigger elements TR1and TR2. The outputs of the AND elements SW1 and SW2 are connected to anOR element OR, the output of which is connected to a trigger input ofthe diverting element DE1. A resistor Rpu connects the trigger input ofthe diverting element DE1 to the second terminal K2.

In a system-level operating state, the first control signal TENT is setto a logic LOW state, so that at the output of the first AND element SW1there is likewise always LOW signal issued, independent of a firsttrigger signal issued at the first trigger output TA1. Correspondingly,the second control signal TEN2 is set to a high state, so that at theoutput of the second AND element SW2, a possible second trigger signalat the second trigger output TA2 is transmitted at the output side.Through the OR member OR, a passed-on trigger signal can be sent to thetrigger input T of the diverting element DE1 in order to produce aconducting connection of terminals K1 and K2.

If, however, the control circuit CTRL detects a chip-level operatingstate, the first control signal TEN1 is set to a HIGH state and thesecond control signal TEN2 is set to a LOW state, so that a firsttrigger signal of the first trigger element TR1 can be transmitted,while a second trigger signal of the second trigger element TR2 isblocked by the second AND element SW2.

FIG. 11 shows another embodiment example of a circuit arrangement basedon the embodiment examples shown in FIG. 9. The first and secondswitchable elements SW1 and SW2 in this embodiment example are designedas inverters, to which the first and second control signals TEN1 andTEN2 are correspondingly delivered at the input side. The inverters SW1and SW2 are each connected at one terminal to the first terminal K1 andat another terminal to the relevant transistor N1 and N2, the controlinput of which is connected to one of the trigger outputs TA1 and TA2.The outputs of the inverters SW1 and SW2 are connected to the triggerinput T of the diverting element DE1.

The transistors N1 and N2 can be controlled by the corresponding triggersignals of the first and second trigger elements TR1 and TR2. In thecase of a system-level operating state, the first control signal TE1again is set to a LOW state, so that the output of the first switchelement SW1 is pulled to the potential at the first terminal K1. Withthat, trigger signals cannot be transmitted to the diverting element DE1via the first transistor N1. The first trigger device TR1 iscorrespondingly deactivated. At the same time in this case, the secondcontrol signal TEN2 again is set to a logic HIGH state, so that thesecond inverter SW2 is pulled downward, in the direction of thepotential at the second terminal K2; the output potential of inverterSW2, however, remains at the potential of the first terminal K1 becauseof the resistor Rpu. As soon as the second transistor N2 is activated orcontrolled by a trigger signal at the trigger output TA2 of the secondtrigger element TR2, the potential at the output of the signal inverterSW2 is pulled to the position of the second terminal K2, so thattriggering of the diverting element DE1 occurs.

Thus, the first trigger element TR1 is deactivated and the secondtrigger element TR2 is activated. With an appropriate switching of thelogic states of the control signals TEN1 and TEN2, thus the firsttrigger element can be activated and the second trigger element TR2deactivated, which corresponds to protection for a chip-level operatingstate.

FIG. 12 shows an alternative embodiment example of a circuit arrangementthat again is based on the embodiment example in FIG. 9. Switchableelements SW1 and SW2 that are designed as transistors are provided atthe corresponding trigger outputs TA1 and TA2, and these connect thetrigger outputs TA1 and TA2 to the second terminal K2. The first andsecond switchable elements SW1 and SW2 are controlled via the controlsignals TEN1 and TEN2. Depending on the switching state of theswitchable elements SW1 and SW2, a relevant trigger signal of the firstand second trigger elements TR1 and TR2 can be used to control n-channelfield effect transistors N1 and N2, the outputs of which are connectedto the trigger input T of the diverting element DE1. If one of theswitchable elements SW1 and SW2 is in a conducting state, the potentialat the control input of the corresponding transistor N1 or N2 is at thepotential of the second terminal K2, so that control of the relevanttransistor N1 or N2 is not possible. Activation or deactivation of thefirst and second trigger elements TR1 and TR2 thus takes placeregardless of the switching state of the switchable elements SW1 andSW2. The transistors of the switchable elements SW1 and SW2 in this casecan be designed for a small current load and therefore the spacerequirement in an integrated circuit is smaller.

FIG. 13 shows an embodiment example of trigger elements TR1 and TR2,which can be activated or deactivated by means of control signals TEN1and TEN2 on the basis of the principle of the embodiment example shownin FIG. 9. The first trigger element TR1 comprises a series circuit of acompacitor C1 and a resistor R1 and an amplifier element A1, which isconnected at the input side to the connection junction of resistor R1and capacitor C1. One output of the amplifier element A1 forms the firsttrigger output TA1 or is connected to the first trigger output TA1. Thesecond trigger element TR2 comprises a series circuit of a Zener diodeZ2 and a resistor R2, which are connected between the first and secondterminals K1 and K2. Similar to the first trigger element TR1, a secondamplifier element A2 is connected at a connection junction of the Zenerdiode Z2 and resistor R2, its output forming the second trigger outputTA2 or being connected to it.

The first trigger element TR1 is, via the RC series circuit of elementsR1 and C1, suitable for detecting a preset voltage rise between thefirst and second terminals K1 and K2 and issuing a corresponding triggersignal. The first trigger element TR1 is for this reason especiallysuitable for a chip-level operating state. A duration of a voltage risethat is to be detected can take place, for example by appropriatedimensioning of capacitor C1 and/or resistor R1.

The second trigger element TR2 is, via the series circuit of Zener diodeZ2 and resistor R2, suitable for issuing a second trigger signal inaccordance with a preset threshold voltage between the first and secondterminals. The threshold voltage here is determined in particular by thebreakdown voltage of the Zener diode Z2. The second trigger element TR2is therefore especially suitable for a system-level operating state inwhich the circuit arrangement is installed or put into operation.

A switchable element SW1 and SW2 designed as a transistor is provided ineach case in parallel to resistors R1 and R2 of the first and secondtrigger elements TR1 and TR2, the element being controllable dependingon the first or second control signal TEN1 or TEN2. The trigger outputsTA1 and TA2 are, for example, connected to a trigger input of adiverting element DE1, not shown here. Referring to FIG. 9, the controlsignals TEN1 and TEN2 can be made available from an appropriate controlcircuit CTRL.

In a HIGH state of one of the control signals TEN1 or TEN2, thecorresponding switchable element SW1 or SW2 is controlled so that therelevant resistor R1 and R2 is bypassed. In this case dynamic control ofthe relevant trigger element TR1 or TR2 is no longer possible. Thusagain, by appropriate control of the switchable elements SW1 and SW2,activation or deactivation of the first and second trigger elements TR1and TR2 takes place.

The scope of protection of the invention is not limited to the examplesgiven hereinabove. The invention is embodied in each novelcharacteristic and each combination of characteristics, which includesevery combination of any features which are stated in the claims, evenif this feature or combination of features is not explicitly stated inthe examples.

What is claimed is the following:
 1. A circuit arrangement forprotection against electrostatic discharges comprising: a divertingstructure with a diverting element, which is configured to drain off anelectrostatic discharge between a first and a second terminal; a firsttrigger element, which is configured to issue a first trigger signal inaccordance with a preset voltage rise between the first and secondterminals; a second trigger element, which is configured to issue asecond trigger signal in accordance with a preset threshold voltagebetween the first and second terminals; a first switchable element and asecond switchable element, each of which can take on a first and asecond switching state; and a control circuit, which is configured toactivate a function of the first and second trigger elements via controlof the first and second switchable elements, wherein the divertingelement is configured to connect the first and second terminals inaccordance with the first and/or the second trigger signal, and whereinthe control circuit is set up to determine an operating state of thecircuit arrangement, and if a first operating state is determined, toactivate a function of the first trigger element and to deactivate afunction of the second trigger element, and if a second operating stateis determined, to activate a function of the second trigger element andto deactivate a function of the first trigger element.
 2. The circuitarrangement as in claim 1, wherein the diverting element comprises atleast one of the following: a pnp transistor; a p-channel field effecttransistor; a Zener diode; and an element with a voltage-currentcharacteristic curve that does not have voltage snapback.
 3. The circuitarrangement as in claim 1, wherein the control circuit is set up toactivate and/or to deactivate a function of the first and second triggerelements in accordance with an average potential difference between thefirst and second terminals.
 4. The circuit arrangement as in claim 1,wherein the diverting element comprises an element with avoltage-current characteristic curve that does not have voltagesnapback.
 5. The circuit arrangement as in claim 1, wherein the controlcircuit is set up to control an activation status of the first triggerelement via control of the first switchable element and to control anactivation status of the second trigger element via control of thesecond switchable element.
 6. The circuit arrangement as in claim 1,wherein the first operating state corresponds to a chip levelelectrostatic discharge protection state, and the second operating statecorresponds to a system-level electrostatic discharge protection state.7. The circuit arrangement as in claim 1, wherein the control circuit isset up to determine the operating state based on an average potentialdifference between the first and second terminals.
 8. The circuitarrangement as in claim 1, wherein the diverting element comprises asingle trigger input for receiving the first and the second triggersignal.
 9. A method for operation of a circuit arrangement forprotection against electrostatic discharges, the method comprising:providing the circuit arrangement with a diverting element that is setup to drain off an electrostatic discharge between a first and a secondterminal; generating a first trigger signal in accordance with a presetvoltage rise between the first and the second terminal; generating asecond trigger signal in accordance with a preset threshold voltagebetween the first and the second terminal; determining an operatingstate of the circuit arrangement; transmitting of the first triggersignal if a first operating state is determined in the determining step,and transmitting the second trigger signal if a second operating stateis determined in the determining step, wherein the diverting element iscontrolled with at least one of the first transmitted trigger signal andthe second transmitted trigger signal; and blocking of the secondtrigger signal if the first operating state is determined, and blockingof the first trigger signal if the second operating state is determined,such that the diverting element is controlled with only one of the firsttransmitted trigger signal and the second transmitted trigger signal.10. The method as in claim 9, wherein an average potential differencebetween the first and second terminals is evaluated in the step ofdetermining the operating state.
 11. The method as in claim 9, whereinthe diverting element comprises an element with a voltage-currentcharacteristic curve that does not have voltage snapback.
 12. The methodof claim 9, wherein the diverting element comprises a single triggerinput for receiving the first and second trigger signal.
 13. The methodas in claim 9, wherein the first operating state corresponds to a chiplevel electrostatic discharge protection state, and the second operatingstate corresponds to a system-level electrostatic discharge protectionstate.